About 20 percent of our population seems to have a genetic or inherited factor that increases their chances of developing an autoimmune disease. Several genes together determine the ability to inherit an autoimmune disease. However, genetic predisposition alone is not the only cause.
It seems that other factors need to be present in order to initiate the disease process. It is very important for families with members who have autoimmune diseases to mention their family history when another family member is experiencing medical problems that appear to be difficult to diagnose. There are more than 100 known autoimmune diseases. One of every 5 Americans or 20% of the population has an autoimmune disease.